Maximising performance, minimising contamination

Paul Boughton

Jacques Miéville reveals the best design approach for components to be deployed in dangerous areas

One of the toughest design challenges an engineer faces is choosing components and connectors for equipment to be used where there is a high risk of contamination. Images of people using equipment in decontamination work after a nuclear disaster such as that in Fukushima, or where there has been an Ebola outbreak, readily spring to mind. Design engineers’ priority is finding optimal technical solutions that ensure people’s safety and security. When designing components for use in these dangerous fields, it is essential to choose materials, performances and operational processes wisely.

Nuclear decontamination

Nuclear contamination is one of the main security concerns when working with radioactive materials. A contaminated object can harm operators, so radioprotection is key when designing or using devices that involve handling radioactive materials. Nuclear contaminant can be present in most known states of matter (solid, liquid, gas). Liquid is a concern for lots of equipment because, if spilled, the contaminant spreads uncontrollably on many parts and can easily penetrate cavities. Cleanability is therefore a key factor in offering maximum security to users.

If a radioactive liquid solution spills on a mechanical part, surface diffusion takes place, allowing radioactive ions to slowly migrate from the solution inside the material molecular structure, thus contaminating it. Once radioactive ions have diffused, it is very difficult to remove them whilst preserving the part integrity. The last resort, if decontamination protocols fail, is either surface etching to remove the diffused layer, or leaving sufficient time to let the ions decay naturally.

Sterilisation

Biological and chemical contamination is a major safety concern when working with medical systems and devices, in hospitals, labs or the field. The main challenge is to ensure cleanliness and sterility, in addition to biocompatibility and ease of use. All equipment has foreign material on its surface, including living organisms such as bacteria, viruses or spores, and particles such as minerals or chemicals. Cleanliness means the absence of any foreign material, and sterility means the absence of living organisms. Since a contaminated object can harm patients and medical staff, easy cleaning and sterilisation matter.

Cleaning processes have to reduce surface contamination to below maximum regulatory limits and reduce non-living contaminants. Sterilisation processes have to substantially reduce the bio-burden. Sterilisation methods include: hot processes, e.g. using hot air or vapour (autoclave); cold processes, e.g. using ethylene oxide (EtO), or plasma H202; cold irradiation methods, eg using gamma ray or electron beam (e-beam). For connectors, autoclave, EtO, plasma and gamma are recommended. In some medical fields, such as nuclear medicine that uses many radioactive agents, both radioactive decontamination and sterilisation are required. The use of glove boxes and laboratory equipment is mandatory to manipulate such preparations.

Design guidelines

For robust, reliable components to be used in these fields, Fischer Connectors uses premium grade 316L stainless steel for all exposed parts, thus ensuring the best possible decontamination performance. Stainless steel’s special auto passivation property makes it the best choice to limit surface diffusion. Stainless steel is recommended in highly corrosive environments or where surface diffusion must be avoided. Its high resistance to radiation, temperature and chemicals, coupled to low diffusion rate, makes it ideal for nuclear, chemical and medical applications. The new Fischer Core Series Stainless Steel connectors allow radioactive decontamination and microbiological sterilisation (autoclave, ethylene oxide (EtO), gamma radiation, Steris or Sterrad, Cidex). The company has worked together with HESGE (Geneva University of Applied Sciences) to recommend a cleaning process that gives the best decontamination results on its stainless steel connectors.

There are other ways of reducing contamination risk or damage to equipment used in dangerous environments. Low surface roughness, coupled to a smooth design, improves cleaning efficiency by limiting cavities, thus helping decontaminant liquid flow and efficiency. Compactness reduces surface area, as well as the size and number of connectors required. Sealing prevents leakage and entry of contaminants. Easy handling, including quick, easy connection and de-connection even with one hand or wearing gloves, reduces the risk of spillage.

Other features such as robust keying systems, over-moulded assemblies and protective caps protect the equipment during rough use. An example of an innovative product designed to meet these requirements is the new pin socket version of the Fischer MiniMax series. This high-density, miniature solution offers a combination of power and signal contacts in 19 and 24 pin configurations. This packs more functionality into smaller devices, giving designers greater flexibility within space and weight constraints. With IP68 sealing (2m/24h both mated and unmated), a choice of push-pull, screw lock and quick release locking systems, and many protective feature options, it is ideal for handheld use in healthcare settings or any application that requires accessing multiple protocols via a single connector and easy handling.

In a nutshell, equipment requiring radioactive decontamination and sterilisation needs to be designed from the outset with stringent safety and regulatory requirements in mind. Equipment and operational processes have to be adapted to the specific context of use, as well as to the product and contaminant properties. Premium sealed connectors that offer excellent decontamination and sterilisation performances should be selected, to preserve the user’s safety and security and ensure maximum equipment lifetime. The use of appropriate decontamination, cleaning and sterilisation processes helps to guarantee optimal process repeatability. Other design factors to consider when selecting connectors for use in high-risk environments include low surface roughness, compactness, robust sealing, easy handling and protective features.

For more information, visit www.engineerlive.com/ede

Jacques Miéville is with Fisher Connectors

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